1. Field
Embodiments of the present invention relate to ultrasound (acoustic) data transmission systems, in particular data transmission over wide-band acoustic channels with frequency-dependent multi-path propagation. More specifically, embodiments of the invention relate to data transmission through a wide-band acoustic channel inside a human body.
2. Background
It is well known that a data rate is conventionally proportional to a communication channel bandwidth. For typical acoustic transducers, the frequency bandwidth is about 20% of a carrier. So, for a carrier around 2 MHz, the bandwidth is equal to about 0.4 MHz. This bandwidth allows the system to provide about 800 kbit/s bit rate at the simplest differential quadrature phase-shift keying (DQPSK) modulation scheme with non-coherent signal processing, and about 1600 kbit/s at the very complex 16-quadrature amplitude modulation (QAM) modulation scheme with coherent signal processing.
Image transmission from a capsule inside a human body to an outside receiver requires a very high bit rate exceeding the above-mentioned numbers. Besides, that very high bit rate must be provided at the simplest modulation scheme in the capsule transmitter with minimum power consumption. Therefore, increasing the bit rate is one of the most important and complex tasks of the intra-body acoustic communication technology.